Inner speech—also known as covert speech or verbal thinking—has been implicated in theories of cognitive development, speech monitoring, executive function, and psychopathology. Despite a growing body of knowledge on its phenomenology, development, and function, approaches to the scientific study of inner speech have remained diffuse and largely unintegrated. This review examines prominent theoretical approaches to inner speech and methodological challenges in its study, before reviewing current evidence on inner speech in children and adults from both typical and atypical populations. We conclude by considering prospects for an integrated cognitive science of inner speech, and present a multicomponent model of the phenomenon informed by developmental, cognitive, and psycholinguistic considerations. Despite its variability among individuals and across the life span, inner speech appears to perform significant functions in human cognition, which in some cases reflect its developmental origins and its sharing of resources with other cognitive processes.

Inner speech : development, cognitive functions, phenomenology, and neurobiology.

Traditionally, models of speech comprehension and production do not depend on concepts and processes from the phonological short-term memory (pSTM) literature. Likewise, in working memory research, pSTM is considered to be a language-independent system that facilitates language acquisition rather than speech processing per se. We discuss couplings between pSTM, speech perception and speech production, and we propose that pSTM arises from the cycling of information between two phonological buffers, one involved in speech perception and one in speech production. We discuss the specific role of these processes in speech processing, and argue that models of speech perception and production, and our understanding of their neural bases, will benefit from incorporating them.

Jacquemot C, Scott SK. What is the relationship between phonological short-term memory and speech processing?

TRCs, with taste at the periphery proposed to be encoded via labeled lines [i.e., a sweet line, a sour line, a bitter line, etc. (21)]. Given that Car4 is specifically tethered to the surface of sour-sensing cells, and thus ideally poised to provide a highly localized acid signal to the sour TRCs, we reasoned that carbonation might be sensed through activation of the sour-labeled line. A prediction of this postulate is that prevention of sour cell activation should eliminate CO2 detection, even in the presence of wild-type Car4 function. To test this hypothesis, we engineered animals in which the activation of nerve fibers innervating sour-sensing cells was blocked by preventing neurotransmitter release from the PKD2L1-expressing TRCs. In essence, we transgenically targeted expression of tetanus toxin light chain [TeNT, an endopeptidase that removes an essential component of the synaptic machinery (34–36)] to sour-sensing TRCs, and then monitored the physiological responses of these mice to sweet, sour, bitter, salty, umami and CO2 stimulation. As predicted, taste responses to sour stimuli were selectively and completely abolished, whereas responses to sweet, bitter, salty and umami tastants remained unaltered (Fig. 4 and fig. S5). However, these animals also displayed a complete loss of taste responses to CO2 even though they still expressed Car4 on the surface of PKD2L1 cells. Together, these results implicate the extracellular generation of protons, rather than intracellular acidification (15), as the primary signal that mediates the taste of CO2, and demonstrate that sour cells not only provide the membrane anchor for Car4 but also serve as the cellular sensors for carbonation. Why do animals need CO2 sensing? CO2 detection could have evolved as a mechanism to recognize CO2-producing sources (18, 37)—for instance, to avoid fermenting foods. This view would be consistent with the recent discovery of a specialized CO2 taste detection in insects where it mediates robust innate taste behaviors (38). Alternatively, Car4 may be important to maintain the pH balance within taste buds, and might gratuitously function as a detector for carbonation only as an accidental consequence. Although CO2 activates the sour-sensing cells, it does not simply taste sour to humans. CO2 (like acid) acts not only on the taste system but also in other orosensory pathways, including robust stimulation of the somatosensory system (17, 22); thus, the final percept of carbonation is likely to be a combination of multiple sensory inputs. Nonetheless, the “fizz” and “tingle” of heavily carbonated water is often likened to mild acid stimulation of the tongue, and in some cultures seltzer is even named for its salient sour taste (e.g., saurer Sprudel or Sauerwasser).

http://www.nedsahin.com/wp-content/files/sahin_etal_science2009_ICE_Broca_3-stage.pdf

Sequential Processing of Lexical, Grammatical, and Phonological Information Within Broca's Area

Human infants, unlike even closely related primates, exhibit a remarkable capacity for language learning. Yet how the underlying anatomical network matures remains largely unknown. The classical view is that of a largely immature brain comprising only a few islands of maturity in primary cortices. This view has favored a description of learning based on bottom-up algorithms and has tended to discard the role of frontal regions, which were assumed to be barely functional early on. Here, using an index based on the normalized T2-weighted magnetic resonance signal, we have quantified maturation within the linguistic network in fourteen 1- to 4-month-old infants. Our results show first that the ventral superior temporal sulcus (STS), and not the inferior frontal area, is the less mature perisylvian region. A significant difference of maturation in the STS favoring the right side is an early testimony of the distinctive left-right development of this structure observed during the whole life. Second, asymmetries of maturation in Broca's area were correlated with asymmetries in the posterior STS and in the parietal segment of the arcuate fasciculus, suggesting that an efficient frontotemporal dorsal pathway might provide infants with a phonological loop circuitry much earlier than expected.

https://www.jneurosci.org/content/jneuro/31/4/1500.full.pdf

Early Maturation of the Linguistic Dorsal Pathway in Human Infants

Tool use is the main database to track down behavioral developments in the archaeological record and thus human evolution Working‐memory capacity and modern cognitive potential, however, are no simple and obvious characters in tool behavior Coded in cognigrams, which allow a direct comparison, animal and human tool use can be examined for specific aspects of the working‐memory capacity Detailed studies of tool behavior of wasps, sea otters, bottlenose dolphins, and chimpanzees are presented and compared with the manufacture and use of Oldowan tools and Lower Paleolithic spears Although this shows a wide range of problem‐solution distances, problem solving in animals seems to be restricted to problem complexes for which a solution can be found in spatial and temporal vicinity In human evolution, the complexity of tool behavior increases regarding the number of active foci managed at a time in an action, the number and diversity of operational steps in a problem‐solution complex, and the spatial and te

Working-memory capacity and the evolution of modern cognitive potential: implications from animal and early human tool use

The phonological loop—here referred to as a specialized auditory‐vocal sensorimotor circuit connecting posterior temporal areas with the inferior parietal lobe (Brodmann’s areas 40 and 39) and the ventrolateral prefrontal cortex (Broca’s region, Brodmann’s areas 44 and 45)—is proposed to have been a fundamental element associated with the origin of vocal language in human evolution. This circuit derives from auditory prefrontal networks that preexist in the nonhuman primate but that acquired an unprecedented development in the human brain. The phonological loop overlaps and possibly coevolved with a more ancient circuit involved in hand manipulation and gesture coding (the parieto‐frontal mirror neuron network) and is complementary to a “ventral” auditory circuit connecting the anterior temporal region with anterior Broca’s area (area 45) via the extreme capsule. The development of the phonological loop produced a significant increase in short‐term memory capacity for voluntary vocalizations, which facili...

https://www.jstor.org/stable/10.1086/650525

Sebastián Aboitiz

Papers

The Phonological Loop: A Key Innovation in Human Evolution